This invention relates to a discharge lamp lighting apparatus driven by an internal combustion engine, and more particularly to an internal combustion engine-driven discharge lamp lighting apparatus which is adapted to light a high-pressure discharge lamp such as a high-pressure mercury lamp, a metal halide lamp, a high-pressure sodium lamp or the like.
Conventionally, a synchronous generator driven by an internal combustion engine has been generally used as a power supply unit for lighting an illuminator used in a construction site, that for leisure time amusement or that for disaster relief. Also, a discharge lamp such as a mercury lamp or the like has been recently substituted for an incandescent lamp as an illuminator for a construction site or that for leisure time amusement.
As commonly known in the art, a discharge lamp has negative impedance characteristics, so that once it starts discharge, an impedance thereof is reduced with an increase in current. Thus, a failure in restriction of the current causes an unrestricted increase in discharge current, leading to breakdown of the discharge lamp. In order to avoid such a problem, a conventional discharge lamp lighting apparatus driven by an internal combustion engine includes a ballast including a leakage transformer or a choke coil arranged between a power supply and the discharge lamp, to thereby apply a power voltage through the leakage transformer or choke coil to the discharge lamp.
Also, lighting of a high-pressure discharge lamp such as a high-pressure mercury lamp, a metal halide lamp or the like requires to apply a high voltage across the discharge lamp during starting of the discharge lamp, so that a pulse generation circuit is provided for generating a high-voltage pulse during starting of the discharge lamp.
A pulse generation circuit arranged for this purpose in the conventional discharge lamp lighting apparatus is constructed so as to provide a resonance circuit utilizing an impedance of the ballast during starting of the discharge lamp, to thereby generate a high-voltage pulse.
Thus, the conventional internal combustion engine-driven discharge lamp lighting apparatus requires to arrange the ballast in addition to the generator, leading to an increase in cost.
Also, the ballast serves as an inductive load, to thereby be deteriorated in power factor, so that arrangement of the ballast unavoidably causes an increase in burden on the generator.
Further, arrangement of the ballast between the generator and the discharge lamp causes an inrush current in a large amount to be flowed through an armature coil of the generator during starting of the discharge lamp, resulting in the generator being restricted to driving of a lamp load at a level only about one half to one third as large as rating of the generator, so that the generator is required to be increased in capacity, leading to an increase in cost.
Furthermore, when the discharge lamp lighting apparatus is so constructed that a voltage of the generator driven by an internal combustion engine is applied to the discharge lamp through the ballast and the pulse generation circuit for generating a high-voltage pulse utilizes an impedance of the ballast, the high-voltage pulse is applied directly to the armature coil of the generator. This requires to increase a degree of insulation of the armature coil of the generator, leading to an increase in cost of the generator correspondingly.
Moreover, in the conventional discharge lamp lighting apparatus wherein the high-voltage pulse generation circuit is constructed utilizing an impedance of the ballast while using the internal combustion engine-driven generator as a power supply therefor, a pulse current is flowed through the armature coil of the generator during starting of the discharge lamp, to thereby cause loss in the armature coil, resulting in a failure to fully or satisfactorily utilize energy of the high-voltage pulse.